Bananas are radioactive. This is because they naturally contain high amounts of Potassium and a certain percentage of that is the radioactive Potassium-40. This apparently also causes trucks with bananas to be triple checked at borders in order to prevent the proliferation of nuclear weapons that could be smuggled under a pile of bananas (I couldn’t find a link for that unfortunately, take that info with a grain of salt). Bananas are therefore often used in popular science articles to give people an intuitive sense of radiation doses. Randall Munroe from xkcd.com compiled the Banana Radiation chart and it is fantastic.